toddalin
08-24-2019, 12:27 PM
I've been dealing with a suck-out in the Ethyl Mermans ~250Hz. I get it on both the 18" and 10" (not so much on the L300s), close in frequency (adjacent band on the RTA 1/6th octave apart) and I attribute it to some room bounce be it floor or wall or ???
I was trying to determine a method to reduce floor bounce cancellation. Modern methodology stacks smaller woofers so the distance to the floor varies spreading this over a larger area.
I decided to make a Karlson-style baffle to go in front of the JBL 2241H (18" woofer). I have a bunch of "foam core board" given to me by a JBL Forum member. I cut a piece for a firm fit over the grill and put it in place.
There was still plenty of volume even with everything "buttoned up." Just for laughs, I ran the RTA in the seating position and was truely amazed at the results. Sure there was a slight lost of volume (primarily from reducing the peaks), but the 18" has so much to begin with it didn't matter. The bounce was mostly removed and the whole band was much smoother. Maybe some loss of the deepest bass, but I think that just cutting away the foam core in front of the ports can fix that.
OK, pics are worth thousands of words, so:
The set-up with the foam core in place and mic in position on the couch. We are just doing one speaker here.
http://www.audioheritage.org/photopost/data//500/medium/DSC_000113.JPG
A nice tight fit.
http://www.audioheritage.org/photopost/data//500/medium/DSC_000211.JPG
The spectrum.
http://www.audioheritage.org/photopost/data//500/medium/DSC_000317.JPG
Compressed to show the peaks better.
http://www.audioheritage.org/photopost/data//500/medium/DSC_00105.JPG
Remove the foam core.
http://www.audioheritage.org/photopost/data//500/medium/DSC_000413.JPG
The spectrum.http://www.audioheritage.org/photopost/data//500/medium/DSC_000510.JPG
And compressed.
http://www.audioheritage.org/photopost/data//500/medium/DSC_00086.JPG
Which would you rather listen too?
I was trying to determine a method to reduce floor bounce cancellation. Modern methodology stacks smaller woofers so the distance to the floor varies spreading this over a larger area.
I decided to make a Karlson-style baffle to go in front of the JBL 2241H (18" woofer). I have a bunch of "foam core board" given to me by a JBL Forum member. I cut a piece for a firm fit over the grill and put it in place.
There was still plenty of volume even with everything "buttoned up." Just for laughs, I ran the RTA in the seating position and was truely amazed at the results. Sure there was a slight lost of volume (primarily from reducing the peaks), but the 18" has so much to begin with it didn't matter. The bounce was mostly removed and the whole band was much smoother. Maybe some loss of the deepest bass, but I think that just cutting away the foam core in front of the ports can fix that.
OK, pics are worth thousands of words, so:
The set-up with the foam core in place and mic in position on the couch. We are just doing one speaker here.
http://www.audioheritage.org/photopost/data//500/medium/DSC_000113.JPG
A nice tight fit.
http://www.audioheritage.org/photopost/data//500/medium/DSC_000211.JPG
The spectrum.
http://www.audioheritage.org/photopost/data//500/medium/DSC_000317.JPG
Compressed to show the peaks better.
http://www.audioheritage.org/photopost/data//500/medium/DSC_00105.JPG
Remove the foam core.
http://www.audioheritage.org/photopost/data//500/medium/DSC_000413.JPG
The spectrum.http://www.audioheritage.org/photopost/data//500/medium/DSC_000510.JPG
And compressed.
http://www.audioheritage.org/photopost/data//500/medium/DSC_00086.JPG
Which would you rather listen too?